1. Field of the Invention
The present invention relates to an image forming system.
2. Description of the Related Art
Conventionally, an image forming device that forms a transfer nip by bringing a transfer member into contact with the surface of an image bearer, applies transfer bias output from a transfer bias power supply to the transfer member, and transfers a toner image on the image bearer to a recording member conveyed to the transfer nip is known.
The image forming device described in Japanese Patent Application Laid-open No. 2012-42641 includes a photoconductor, which is a rotatable image bearer on which a toner image is formed, a transfer roller, which is a rotatable transfer member that comes into contact with the photoconductor and forms a transfer nip, and a power supply that applies bias to the transfer roller. The toner image on the photoconductor is transferred onto a sheet, by passing the sheet through the transfer nip, and applying transfer bias having a polarity reverse to the regular charge polarity of the toner to the transfer roller from the power supply. A transfer cleaning operation for cleaning the transfer roller is also executed as an inter-sheet operation, performed when at least one of inter-sheet areas that exist on the photoconductor passes through the transfer nip during a successive image forming period. In the transfer cleaning operation, while the photoconductor and the transfer roller are rotated, cleaning bias having the same polarity as the regular charge polarity of the toner is applied to the transfer roller from the power supply, and the transfer roller is cleaned by electrostatically moving the toner adhering on the transfer roller to the photoconductor.
An image forming system that ejects a sheet, on which an image is formed by the image forming device such as the above, from the image forming device to a post-processing device, and that can selectively execute a post-processing such as a binding processing and a folding processing on the sheet by the post-processing device is also known.
In the image forming system, to extend an interval between the sheets ejected from the image forming device to the post-processing device, so as to ensure post-processing time in the post-processing device, the length of the inter-sheet area is extended in the rotating direction of the photoconductor, compared with that when the post-processing is not performed in the post-processing device. Therefore, when the post-processing time is increased, an inter-sheet time, which is time that the inter-sheet area takes to pass the transfer nip, is increased. As a result, the inter-sheet time sometimes becomes longer than the time required to sufficiently clean the transfer roller by performing the transfer cleaning operation. When the post-processing that significantly increases the inter-sheet time as described above is performed as the inter-sheet operation, if the photoconductor and the transfer roller are kept rotating exceeding the time required to sufficiently clean the transfer roller by performing the transfer cleaning operation, the lives of the photoconductor and the transfer roller are shortened.